1. Field of the Invention
The present invention relates to a recording medium drive managing recordation or storage of information in a recording medium. In particular, the invention relates to a recording medium drive including a swinging arm, a head suspension extending forward from the front end of the swinging arm, a head slider, and a microactuator capable of changing the attitude of the head slider relative to the head suspension.
2. Description of the Prior Art
As disclosed in Japanese Patent Application Publication 11-273041, for example, a well-known head assembly sometimes includes piezoelectric actuators interposed between a head slider and a head suspension. A first common attachment piece is fixed to the head suspension in the head assembly. A pair of parallel piezoelectric actuators extend from the first common attachment piece toward the head slider. The tip ends of the respective piezoelectric actuators are coupled to a second common attachment piece fixed to the head slider. The head slider is allowed to swing around the first common attachment piece in response to expansion and shrinkage of the piezoelectric actuators. The swinging movement of the head slider thus realizes a fine or smaller displacement of the head slider in the radial direction of a magnetic or hard disk. The fine displacement of the head slider enables a read/write head on the head slider to follow recording tracks on the magnetic disk at a higher accuracy.
An electric or servo signal is supplied to the piezoelectric actuators for servo controlling the swinging movement of the head slider. If the frequency of the servo signal gets higher, the head slider can be positioned on the recording tracks at a still higher accuracy. An improved accuracy of positioning the read/write head leads to an increased density of recordation over the magnetic disk.
The head slider and the piezoelectric actuator establish a vibration system. Accordingly, if the frequency of the servo signal coincides with the natural frequency of the vibration system, the head slider should suffer from an abnormal displacement, namely, resonance. In this case, the position of the head slider cannot be controlled. If the natural frequency of the vibration system is raised, the frequency range of the servo signal can be expanded.
It is accordingly an object of the present invention to provide a head assembly contributing to expansion of the frequency range of an electric signal supplied to a piezoelectric actuator.
According to the present invention, there is provided a head assembly comprising: a support member; a head slider; and a piezoelectric actuator set disposed between the support member and the head slider for establishing a standard attitude of the head slider when supply of an electric signal is cut off, wherein said piezoelectric actuator set generates a couple changing an attitude of the head slider around a rotational axis only in a predetermined direction.
The head assembly of this type utilizes the rotation of the head slider so as to accomplish a fine or smaller movement of a head or transducer element. The moment of inertia can be reduced in the head slider during rotation as compared with the case where the head slider is moved based on a swinging movement. Only a smaller moment acts on individual piezoelectric actuators of the piezoelectric actuator set, so that the natural frequency can be raised in the vibration system comprising the head slider and the piezoelectric actuator set. The frequency of the electric signal or servo signal can be set over a wider frequency range.
Moreover, the head assembly simply changes the attitude of the head slider around the rotational axis only in the predetermined direction from the standard attitude. As compared with the case where the attitude of the head slider is changed in at least two directions from the standard attitude, it is possible to simplify the structure of the piezoelectric actuators of the piezoelectric actuator set. Since the piezoelectric actuator set may include few piezoelectric actuators, it is possible to reduce the number of electric terminals, such as golden balls, connected to the piezoelectric actuator set. The electric signal can reliably be supplied to the piezoelectric actuator set with a simplified structure.
For example, the piezoelectric actuator set may include: a first elongated piezoelectric actuator extending in a first direction, a base end of the first elongated piezoelectric actuator being attached to the support member, a tip end of the first elongated piezoelectric actuator being attached to the head slider; and a second elongated piezoelectric actuator extending in a second direction antiparallel to the first direction, a base end of the second elongated piezoelectric actuator being attached to the support member, a tip end of the second elongated piezoelectric actuator being attached to the head slider. In particular, the first elongated piezoelectric actuator is allowed to shrink in a first direction upon supply of the electric signal, while the second elongated piezoelectric actuator is allowed to shrink in a second direction, antiparallel to the first direction, upon supply of the electric signal. The head assembly of this type solely utilizes a pair of the elongated piezoelectric actuators so as to realize the rotation of the head slider. The structure of the head assembly can be simplified. The first and second elongated piezoelectric actuators may be located symmetric to each other around the rotational axis so as to realize the generation of a couple.
The head assembly may further comprise: first outside electrodes connected to the base ends of the first and second elongated piezoelectric actuators, respectively; and second outside electrodes extending from the tip ends toward the base ends along surfaces of the first and second elongated piezoelectric actuators, respectively. The head assembly of this type allows the first and second outside electrodes to be located only near the base ends of the respective elongated piezoelectric actuators. Terminals such as golden balls can thus easily be connected or bonded to the first and second elongated piezoelectric actuators. The electric signal can be supplied to the first and second elongated piezoelectric actuators with a simple structure.
Each of the first and second elongated piezoelectric actuators may comprise: first inside electrode layers connected to the first outside electrode at outer ends of the first inside electrode layers near the base end of the elongated piezoelectric actuator, said first inside electrode layers extending from the outer ends toward the tip end of the elongated piezoelectric actuator; second inside electrode layers each disposed between adjacent ones of the first inside electrode layers and connected to the second outside electrode at outer ends of the second inside electrode layers near the tip end of the elongated piezoelectric actuator, said second inside electrode layers extending from the outer ends toward the base end of the elongated piezoelectric actuator; and active piezoelectric transducer layers interposed between the first and second inside electrode layers. When the electric signal is supplied to the active piezoelectric transducer layers, the active piezoelectric transducer layers shrink in the d31 direction, perpendicular to the direction of the electric signal, based on a so-called lateral effect. Specifically, the active piezoelectric transducer layers shrink along the first and second inside electrode layers. The shrinkage of the piezoelectric actuators is thus realized. The amount of the shrinkage depends upon the intensity of the applied voltage. The active piezoelectric transducer layer may be made from a piezoelectric material such as PNN-PT-PZ, for example.
Each of the first and second elongated piezoelectric actuators may further comprise an inactive piezoelectric transducer layer superposed over an outer surface of at least one of the first and second inside electrode layers between the trailing and tip ends of the elongated piezoelectric actuator. The active piezoelectric transducer layers solely shrink in the first and second elongated piezoelectric actuators upon supply of the electric signal. The inactive piezoelectric transducer layer serves to prevent the active piezoelectric transducer layers from shrinkage. As a result, the elongated piezoelectric actuators of this type are allowed to bend upon supply of the electric signal. The bending and the shrinkage cooperate to generate the aforementioned couple. The inactive piezoelectric transducer layer may be made from the material identical to that of the active piezoelectric transducer layer.
The head assembly of the type described above may be incorporated in a magnetic disk drive such as hard disk drive (HDD), and the other types of recording disk drives.